IMHO, if all you are trying to do is improve the sound of your recording by using a console for summing instead of your computer, I don't think its worth the effort. On the other hand, even if the console and the DAW sound exactly alike when summing audio, I would find working on a semi-full featured console like the 600 to be a huge improvement. Real faders, one knob per function, massive amounts of I/O, a reasonably comprehensive master section......the physical act of mixing on this console is a few million percent more pleasant than mouse-mixing. The 600 is no API, Neve or even Trident, but I spent a good amount of time on one and you can certainly get the job done using one of these, especially if you have a nice outboard collection.
But no, neither the Soundcraft 600, or any other console that costs less than a small house, is going to noticeably improve your audio signal compared to summing in your DAW. I think folks are mixing analog for the wrong reason, I believe that you can get a good result either way, if you have great converters, top quality outboard, etc. But the actual manual work of creating a mix is both pleasant and intuitive on a good desk. It reminds me of accounting when done in the box.
(to be fully honest about my experiences, the 600 that I have done extensive work on had been given the full Audio Upgrades treatment. According to the owner, all the modules, both input and master had been mod'd by Mr. Williams. I have worked on other, stock 600s but never more than a day or two for each. So I can't really comment on a stock unit.)
